Scan mode is a special way of waveform display, when the oscilloscope is at slow time-base. As the oscilloscope screen refresh cycles are basically the same, when the time base of the oscilloscope is larger, i.e. at slow time-base, the time of acquiring a frame of waveform will be greater than the screen refresh circle. At this point, all the data acquired in the screen refresh cycle are read out, and still can't form a frame of complete waveform, thus, “scan mode” is adopted to display the waveform.
The waveform display in scan mode is that the newly acquired waveform appears at the far right of the screen and the previously acquired waveform moves to the left for the corresponding length of time. When the waveform is continuously updated, a waveform that moves from the right to the left will be displayed on the screen of the oscilloscope.
The display technology of modern digital storage oscilloscope (DSO) is also constantly upgrading, the high-end digital storage oscilloscopes at the present stage generally have fluorescent waveform display. The fluorescence waveform display is realized through the three-dimensional (3D) mapping, i.e. the probability statistics and superposition of multiple frames of waveform. The advantages of the fluorescent waveform display is that it not only shows the variation of waveform amplitude with time, but also shows the probability of waveform amplitude at a specific time.
However, the three-dimensional mapping needs to acquire multiple frames of waveform in one screen refresh cycle, and in the traditional scan mode, the digital storage oscilloscope at slow time-base will spend a long time acquiring a frame of waveform, a whole frame of waveform can't be acquired in one screen refresh cycle. Therefore, multiple frames of waveform for three-dimensional mapping can't be obtained in scan mode, then there is no fluorescent waveform display on the screen of digital storage oscilloscope.